1. Field of the Invention
The present invention relates to a traffic information system, and more particularly, to an apparatus and method for collecting traffic information on roads by which a time and a speed required for traveling a link of a road are detected and collected on a real time basis regardless of a location or an environment of the road. An average travel time and an average travel speed by links of the entire road are computed and managed by time zones, which are constantly provided to a driver so as to inform him of the extent of traffic congestion on roadways immediately and accurately.
2. Description of the Background Arts
Recently, according to industrial development, supply of vehicles has been explosively increased, which makes drivers to take more time and distance for driving. Also, as the road networks become complicated as they are expanding, there are high possibilities for the drivers to take an unfamiliar road to drive.
The rapid increase in the supply of the vehicles compared to the relatively little road leads to the severe traffic congestion in roads, causing an enormous damage to the national economy.
In order to reduce such a damage, it is necessary to quickly and accurately detect the extent of traffic congestion of the entire road and inform drivers of it, so that they can be dispersed to less congested roads or less crowded time zones in their use of roads. This would be quite advantageous in view that the limited road resource is effectively utilized without any investment.
Accordingly, it is desirable to collect traffic information on the entire road, so as to recommend to the drivers the fastest route to an intended destination before his starting or inform the drivers when they are unfortunately caught in heavily congested roads or in complicated downtown traffic networks.
Recently, there have been presented many traffic information collection systems for collecting traffic flow information on the entire road by time zones, for an effective management.
The traffic information collection systems are characterized in that positions of roads and facilities on the map are digitized and stored in a memory, position information on a vehicle mounting a terminal is collected and matched with links as digitized on the map of the memory, thereby guiding a travel time and a travel speed of each link of the entire road.
The traffic information collection systems mostly employ a global positioning system (GPS).
The GPS system in use for the traffic information collection system is a space-based satellite radio navigation system developed by the U.S. Department of Defense which includes an intentional error in transmission in order to prevent any military use by other countries.
According to this system, by receiving radio signals transmitted from at least three or four satellites among many GPS satellites having an atomic clock placed in the orbit, a distance to the satellite is obtained from the travel time of the radio signals and a speed measurement is available by using the Doppler effect.
As aforementioned, though the global positioning system (GPS) was initially developed for military use, as it was recognized to have a high utility value for civil vehicle means, the satellites started a service for civil use, by transmitting radio signals for measurement including the intentional range error.
By applying the global positioning system to the traffic information collection system, information on a vehicle operation, such as a distance to the destination and a time required, can be obtained.
Typically, the range error contained in the signal receiving from the GPS satellite is approximately in the range of 100 m to 2km.
FIGS. 1 and 2 are exemplary views of an apparatus for collecting traffic information by using the global positioning system in accordance with a conventional art.
The apparatus for collecting traffic information of the conventional art includes a plurality of GPS satellites 10 for transmitting GPS signals including time information; a GPS terminal for receiving, computing and transmitting the position information of the vehicle as transmitted from the GPS satellites 10; a vehicle 12 (termed as `probe vehicle`, hereinafter) mounting the GPS terminal; a communication relay unit 12 for relaying the signal transmitted from the GPS terminal 11; and a service center 108 for receiving the position signal of the relayed probe vehicle, and computing and managing an average travel time and travel speed of the probe vehicle 12.
As shown in FIG. 2, the GPS terminal 11 for computing the position information on the basis of the radio waves as transmitted from the GPS satellites 10 and transmitting the same to the communication relay unit 106 includes a GPS receiver 101 for receiving the GPS signal having the position information on the vehicle and the time information through an antenna 100 from the plurality of GPS satellites 10 and computing the position information of the probe vehicle 12; an operating panel 103 for selecting and inputting corresponding functions; a CPU for analyzing history of the position information periodically transmitted from the GPS receiver 101, to correct a position measurement error, and controlling the overall operation of the system; a wireless communication module 104 for modulating the position information on the probe vehicle for which the position error was corrected, and transmitting the same through the antenna 105.
The GPS receiver 101 of the GPS terminal 11 includes a frequency down converter 101a for frequency down converting the plurality of GPS signals in the different range of a few GHz(substantially 1.about.2 GHz)as received through the antenna to baseband signals; a GPS tuner 101b for extracting only a GPS signal corresponding to the current position of the vehicle from the frequency down converted baseband signals; a position operation unit 101c for computing an absolute coordinate of latitude, longitude, altitude and a standard time with the extracted GPS signal and outputting current position information on the probe vehicle 12 to the CPU 102.
The wireless communication module 104 of the GPS terminal 11 includes a local oscillator 104b for generating an oscillation frequency under the control of the CPU 102; a modulator 104a for modulating the position information of the probe vehicle 12 of which position error was corrected by the CPU; a transmitting/amplifying unit 104c for amplifying the modulated signal to a sufficient amplitude; and a transmission power amplifier 104d for power-amplifying the amplified transmission signal to a sufficient intensity and transmitting the same through the antenna 105.
As shown in FIG. 2, the service center 108 for receiving the position information on the probe vehicle 12 from the GPS terminal 11 and computing and managing the average travel time and travel speed of the probe vehicle 12 includes a communication server 108a for receiving the transmission signal of the GPS terminal 11 being relayed through the communication relay unit 106, and extracting the position information on the probe vehicle 12; a map server 108b for digitizing the extracted position information, and mapping it with the link on the electronic map to detect a travel time and a travel speed in the link; and a database server 108c for systematically managing the data related to the travel time and the travel speed of each link that was collected by operating the probe vehicle 12 from the map server 108b.
FIG. 3 is a signal flow chart illustrating a method for collecting traffic information of FIG. 2 wherein, when the probe vehicle is moving, the GPS signals transmitted from the plurality of the GPS satellites 10 are received by the GPS terminal 11 mounted in the probe vehicle 12 to compute the position of the probe vehicle and transmit it, and the service center 108 collects the transmitted position information on the probe vehicle 12 through the communication relay unit 106 to analyze the traffic flow information on the road, to thereby systematically store and manage it.
The operation of the apparatus for collecting traffic information using the global positioning system constructed as described above in accordance with the conventional art will now be explained in detail.
In the state that the GPS terminal 11 of the apparatus for collecting traffic information adapting the global positioning system is actuated by the operation of function keys of the operating panel 103 (stage: ST10), when the probe vehicle 12 starts moving (stage: ST11), the CPU 102 actuates the GPS receiver 101 and the wireless communication module 104.
Then, the GPS receiver 101 receives the radio waves from the plurality of GPS satellites 10 placed in the orbit and computes the position of the probe vehicle 12.
In other words, the plurality of GPS satellites placed in the orbit, that is, for example, 20 GPS satellites 10, transmits the GPS radio waves having the position information on the probe vehicle 12 and the time information.
As shown in FIG. 2, the GPS radio waves transmitted from the plurality of GPS satellites 10 are received by the GPS receiver 101 of the GPS terminal 11 mounted in the probe vehicle 12 to be processed.
As shown in FIGS. 1 and 2, the GPS receiver 101 of the GPS terminal 11 mounted in the probe vehicle 12 receives the radio waves from at least three or four GPS satellites 10 (preferably four GPS satellites) among many GPS satellites placed in the orbit through a radio wave receiving unit such as, for example, an antenna 100 (stage: ST12) and supplies the same to the frequency down converter 101a.
The frequency down converter 101a frequency down converts the received GPS radio waves in the range of a few GHz to baseband signals and then provides them to the GPS tuner 101b.
The GPS tuner 101b extracts a baseband signal that is the most suitable to its own position among the baseband signals for each GPS signal inputted through the frequency down converter 101a, and provides it to the position operation unit 101c.
The position operation unit 101c computes an absolute coordinate of the probe vehicle 12 on the basis of each baseband signal tuned and inputted by the GPS tuner 101b, that is, on the basis of the latitude, the longitude, the altitude and a standard time (stage: ST13), and provides it to the CPU 102 (to be described).
As aforementioned, the GPS signals transmitted from the plurality of satellites 10 include information on time as transmitted from the satellites.
The travel time taken for each of the radio waves to reach the probe vehicle 12 from each of the plurality of the GPS satellites is different to each other due to the difference in the distances between the probe vehicle 12 and each of the GPS satellites 10. In this respect, by using the travel time of each GPS signal from the GPS satellites to a specific probe vehicle 12 over a reference coordinate, the absolute coordinate value for the specific probe vehicle 12 can be obtained.
Accordingly, the CPU 102 corrects the error of the position information on the probe vehicle 12 inputted after being periodically and continuously computed by the position operation unit 101c of the GPS receiver 101, controls the local oscillator 104b of the wireless communication module 104 so as to transmit the corrected position information signal to the public network with very short cycle, i.e., 1 second cycle, and provides the position information signal to the modulator 104a of the wireless communication module 104.
The position information signal of the probe vehicle 12 corrected and outputted from the CPU 102 is mixed with the oscillation frequency of the local oscillator 104b in the modulator 104a, and amplified to a sufficient amplitude by the transmitting/amplifying unit 104c of the wireless communication module 104, and then provided to the transmission power amplifier 104d.
The transmission power amplifier 104d of the wireless communication module 104 power-amplifies the position information signal inputted after being frequency-modulated in very short cycle to a sufficient intensity, and transmits the same to the public network through the antenna 105 (stage: ST14).
The signal transmitted from the GPS terminal 11 of the probe vehicle 12 is received by the service center 108 through the communication relay unit 106 to be processed.
The service center 108 includes the communication server 108a, the map server 108b and the database server 108c.
The communication server 108a of the service center receives the transmission signal of the probe vehicle 12 relayed to the public network through the communication relay unit 106 through the antenna 107, and periodically extracts only the position information of the probe vehicle 12 from the received transmission signal and supplies the same to the map server 108b (stage: ST15).
The map server 108b includes a compact disk player loading the CD ROM.
The compact disk ROM stores the positions of the roads and facilities on the map.
Accordingly, as the position information is inputted through a communication line, the map server 108b loads the electronic map recorded on its own recording medium such as the compact disk to read it.
The position information on the probe vehicle 12 as extracted and inputted is map-matched with a starting point and an ending point of each link on the electronic map, so that time and speed required for the probe vehicle 12 to travel in each link are periodically computed (stage: ST16).
The data related to the travel time and travel speed of the probe vehicle 12 computed by links in the map server 108b is periodically provided to the database server 108c through the communication line.
The database server 108c systematically stores and analyzes the data related to the travel time and the travel speed in each link that is collected over the operation of the probe vehicle 12 from the map server 108b (stage: ST17), to compute an average travel time and an average travel speed in the link (stage: ST18).
In that manner, the average travel time and speed in the link are computed and managed by time zones, and transmitted to the vehicle mounting the car navigation system, so that the traffic flow on the roads can be notified, and the fastest route to the destination can be recommended to the driver before starting traveling.
As to the apparatus for collecting traffic information using the global positioning system in accordance with the conventional art as described above, it is noted that the radio waves transmitted from at least three GPS satellites among the plurality of GPS satellites placed in the orbit is received by the probe vehicle to thereby computes the position of the vehicle, and computed position information on the probe vehicle is wirelessly collected by the map server of the service center and map-matched with the starting point and the ending point of the link on its own electronic map, thereby computing and managing the average time and speed taken for traveling in each link of roads.
However, the apparatus for collecting traffic information using the global positioning system in accordance with the conventional art has disadvantages in that since the GPS satellite signal intentionally includes an error, in case that the position of the vehicle is sensed by using the GPS terminal, the position error is extensively generated in the range of 100 m to 2 Km, making it difficult to accurately map-match with the starting point and the ending point of the link.
Also, in an area where there is a tunnel, or in a mountainous area, or in the downtown area where there are many tall buildings, since less than four satellites are available for simultaneously receiving the radio waves to the probe vehicle, the position error for the probe vehicle is so broad-ranged, and thus, its accurate position of the vehicle is hardly detected.
In addition, besides the problem caused by the GPS signal error, another error is generated with map-matching the starting point and the ending point of the link because of the communication cycle in transmitting the position information on the probe vehicle to the service center. Also, in order to reduce this error, the position information on the probe vehicle is required to be transmitted to the service center at very short intervals, which disadvantageously causes a problem in that the expense for communication is much increased.
Furthermore, use of a differential GPS may be considered as one method for reducing the measurement error of the probe vehicle with respect to the GPS radio waves transmitted from the plurality of satellites, which, however, also increases the expense.